Powder metallurgy is a commonly-seen fabrication technology of metallic products. The powder thereof has an average particle diameter of about 70 μm, which is a coarse powder having large space among particles. The large space among particles results in the large porosity and poor mechanical properties of the sintered products. Compared with finer powder, coarse powder has longer diffusion length, which causes poor homogeneity of the alloying elements thereof. Further, coarse powder has smaller surface area, which leads to weaker sintering driving force, lower sintered density and poorer product quality.
A fine iron powder, such as a carbonyl iron powder, has high specific surface area and superior sinterability and thus can be sintered to a high density. However, fine powder is poor in flowability and hard to flow into the mold cavity. Thus, the powder metallurgy thereof is hard to automate. Carbonyl iron powder is fabricated in a high-temperature and high-pressure chemical reaction. Therefore, carbonyl iron powder has the disadvantage of high cost. Fine iron powder can also be fabricated with a water atomization method. However, the iron powder fabricated thereby still has the problem of poor flowability, low yield and high cost. The fine iron powders fabricated with other conventional methods have same drawbacks.
To solve the above-mentioned problems encountered as one desires to produce a powder with high compressibility, good sinterability and homogeneity, the Inventors of the present invention had proposed a solution involving “Sinter-Hardened Powder and Sintered Body Thereof” disclosed in a Taiwan patent No. I294318 and a German patent No. DE102006027851, wherein the sinter-hardened powder comprises iron, carbon, nickel, chromium and molybdenum with iron being the primary constituent. The sinter-hardened powder adopts a fine powder having a particle size of 0.1-3 μm, such as a carbonyl iron powder. After spray granulation, the powder has flowability and can be shaped with a dry-compression process. After sintering, the product has high density, and the alloying elements thereof are homogenously distributed. Because of adopting carbonyl iron powder, the sinter-hardened powder still has the problem of high cost. While containing carbon, the carbonyl iron powder has high hardness and poor compressibility, resulting in low green compact density, likely to abrade the molds, and thus unfavorable to industrial application.